The present invention relates to the art of aircraft cover methods and apparatuses, and more particularly to covers for helicopter rotors.
Modern civilian and military helicopters utilize, nearly exclusively, composite blades. Typical composite blades utilize a Nomex honeycomb core with bonded glass skin, such as one or more layers of fiber reinforced plastic, forming the aft fairing portion of the blade. For further reinforcement, Kevlar, carbon or glass fibers are used. The Nomex core is oriented with the open lines of the cells bonded to the top and bottom skins. D-shaped spars, comprising a glass lay-up with a titanium erosion strip, provides structural support within the blades. The spars are bonded together by epoxy or other adhesive material.
Civilian and military helicopters deployed in warm regions, particularly in desert regions, are subjected to the adverse effects of prolonged exposure to direct sunlight. While most helicopters have been designed to operate in extreme temperature conditions, for example, modern day helicopters have been designed to operate in temperature conditions exceeding 130xc2x0 F., it generally inadvisable to subject the helicopter to extreme temperature conditions for prolonged periods of time. Specifically, high temperatures resulting from absorbing the sun""s infrared rays cause bonding deterioration and delamination of helicopter rotor blade components. Debonding is the disintegration of the epoxy or other adhesive materials between spar connections, and delamination is the peeling of layers of the composite skin forming the outer surface of the rotor blade. Both problems contribute to premature rotor blade failure, particularly when under the high wind sheer and vibrations inherent with helicopter operation.
In addition to the ultraviolet effects of the sun, erosion, poor repairs and repeated high cyclical loading exasperates the problem causing minute openings in the skins. The problem is further perpetuated because, in an outdoor environment, helicopters blades are normally tied down placing the top skins of the blades under constant tension and further weakening deteriorated areas of the rotor blade.
Still further, a rotor blade sitting outside in the sun can easily reach 180xc2x0 F. When heated, the air inside the NOMEX honeycomb core expands and leaks out through any fissures in the skin. Upon cooling, the pressure within the honeycomb core will decrease, and air will be pulled back into the blade, along with any moisture present near the surface of the blade, including rain water, condensation and humidity.
Over time, deterioration of the bonding between the spar connections and delamination of the composite layers not only lead to direct failure of the rotor blades, but also indirectly lead to failure of the blade by allowing water to accumulate and store in the blade""s core cavities. Upon significant water accumulation, the track and balance of the rotor blades can become upset, causing operational problems.
Replacement and/or repair of the rotor blades is expensive, time consuming, and requires the highly skilled technician. A replacement blade for a typical military helicopter costs in the neighborhood of between $85,000 and $105,000.
It is known in the art to apply a cover over the rotor hub and rotor blades of a helicopter to provide a shield which mitigates the adverse effects of direct sunlight. For proper function of the cover, it is necessary to consider not only the ability of the cover to reduce aircraft related temperatures, but also other factors such as weight, costs, transportability, ease of installation and removal, resistance to contaminates/chemicals, moisture resistance/breathability, and detectability such as whether detectable infrared signals are created and the degree of glint.
A conventional solution to minimize the effects of excessive exposure to direct sunlight is to house aircraft in containment shelters that shield the aircraft from incident sunlight. However, shelters, either permanent or temporary, often are not practical, interfering with the practical use of the aircraft. For example, aircraft may be deployed in a rapid response condition to underdeveloped locations where contaminate shelters are not readily available. In similar matter, aircraft may be temporarily deployed to satellite locations for limited time durations which make erection of containment facilities non-cost effective. Such shelters are also easily detected by satellite reconnaissance.
Another conventional approach is to drape a canvas cover over the rotor hub and rotor blades of helicopters to provide a shield against direct sunlight. Such canvas covers are difficult to deploy, being bulky and weighty, and often require as many as ten personnel to lift, position, and secure the canvas cover in the proper position. Further, canvas material has a tendency to snag or catch on equipment discontinuities and/or obstructions in the rotor hub area and along the rotor blade, making deployment time consuming. Also, canvas made of non-porous material, tends to maintain moisture and may be moved from proper position by wind conditions or prop wash from adjacent helicopters or aircraft. Most importantly, significant temperature reduction is not achieved through use of a canvas cover.
In response to the unsatisfactory results of conventional covers, the military has sought out new cover configurations and materials to reduce the intense and destructive heat loads presently encountered by aircraft, and to satisfy the other above-listed considerations. These covers failed to provide a complete solution as briefly discussed below:
One such approach is a highly reflective cover comprised of an outer aluminum foil surface bonded to a tight-knit fiberglass fabric inside surface. Although good temperature reduction can be achieved, the cover is very detectable. First, the highly reflective external surface provides tremendous glint. Second, the smooth aluminum foil outer surface sharply reflects infrared signals. Clearly, a cover which enhances the detectability of a covered aircraft is not well suited for military operations. As a further consideration, the aluminum foil is not durable and will debond from the fiberglass inside surface through use and exposure to heat build-up.
Another cover formed of a light weight, highly formable camouflaged material. This cover configuration is largely ineffective in obviating heat build-up, and in some cases may actually contribute to heat build-up.
A further cover is formed of a polyester duck cloth with an optional liner such as a multi-layered quilt with polyester fiber fill and polyester/cotton on either side of a Mylar film. Only moderate temperature reduction was achieved and the bulky cover requires personnel standing on ladders to install.
Additionally, it is important to protect the helicopter, in general, from exposure to the sun""s infrared rays and from the accompanying heat build-up. Unprotected aircraft systems, components, and enclosures can deteriorate from the heat build-up resulting in an increased failure rate of the equipment. Heat build-up is particularly problematic in the cockpit area and tends to degrade avionics equipment and reduces the readiness response of the aircraft (while cooling systems are utilized to bring the avionics equipment within operating ranges). High temperatures also create a cockpit environment that is not conducive to maximum pilot efficiency and performance. Likewise, heat radiating from the helicopter causes discomfort for ground and air crew personnel, diminishing their ability to perform duties.
Accordingly what is needed is for an aircraft cover, and particularly a helicopter rotor blade cover, which protects the rotor blade from the adverse effects from prolonged exposure to direct sunlight, and the associated heat build-up. Additionally needed is for the cover to have minimal detectability, with indistinguishable infrared signature and de minimis glint. Further needed is for the cover to be light weight, cost effective, resistant to contaminates, chemicals, moisture, and be easily transported and stored.
Applicant is aware of the following U.S. Patents concerning aircraft covers.
The McCausland, U.S. Pat. No. 6,109,872, discloses a helicopter rotor cover system to prevent ice formation on the rotors. The system is comprised of a main rotor cover and a tail rotor cover providing an enclosed space around the rotors, a tubular member connecting enclosed spaces of the two covers and a hot air blower to blow hot air into the two covers. The covers of a tubular member are made from a fabric impermeable to water. For ease of installation and removal, the covers may have separate pieces or openings that are joined with hook and loop fabric fasteners. The main rotor blade covers have oval ribs distributed along the rotor blades to reduce the contact area between the blades and the cover to facilitate flow of air.
Deichmann, U.S. Pat. No. 5,179,968, discloses a climatic heat aircraft protective screen to protect aircraft from adverse effects from direct exposure to sunlight while being relatively insensitive to wind conditions. The screen includes a porous canopy having over hanging eve portions and flat portions that are operated to reflect direct sunlight while allowing air to pass therethrough. Radial deployment strips formed from low friction smooth material may be affixed to the underside of the canopy to facilitate deployment thereof over the main rotor blades of a helicopter. Two ropes are attached to the ends of the deployment strips to facilitate deployment and secure the canopy. A containment bag is affixed to the underside of the canopy into which the canopy can be compactly stowed.
Hann, U.S. Pat. No. 3,057,580, discloses a protector to prevent damage to various surfaces of an aircraft such as ailerons, from hail, freezing rain, and the like. The protector includes a U-shaped body which is contoured to fit over an aircraft control member and seal itself in position over the control member to prevent the entrance of moisture between the protector and the control surface. The U-shaped body is a molded fiberglass member of lightweight construction and easily handled by an operator.
The principal object of the present invention is to provide a device that protects aircraft systems, particularly helicopter rotor blades, from the effects of infrared solar radiation.
Another object of the invention is to provide a device that reduces the heat load applied to a rotor blade due to exposure to sunlight.
A further object of this invention is to provide a device that has minimal detectability, in particular, indistinguishable infrared signature and glint.
Another object of this invention is to provide a device that can be stowed in minimal space and is easily transportable.
A further object of this invention is to provide a device that is resistant to contaminates, chemicals and is water repellant.
Another object of this invention is to provide a device that is simply and quickly installed on, and removed from, a rotor blade by one person.